feat(docker): expose the eBPF time-window filter on kernel links

uBridge's window mode gained the semantics the B.2 spec asked for —
`tc window_drop <if> <start> <outage> <pct> [<period> [<jitter>]]`: a
single outage that traffic passes before *and* after, recurring flaps
with period >= outage, and a per-cycle jitter — so the kernel-only
`window_drop` filter type is now exposed:

- validation mirrors the tc grammar (3-5 params, ranges, period >=
  outage, jitter cap) and adds window_drop to KERNEL_ONLY_FILTERS;
  filter_inactive_filters keeps start=0 — unlike every other filter a
  zero first parameter means "the outage starts now", not "disabled".
- `_ubridge_apply_ebpf_drops` sends `tc window_drop` (positional
  pass-through) and turns the mode off explicitly when absent, under the
  same ebpf=1 gate.
- FILTERS entry (Start/Outage/Chance/Period/Jitter) + available_filters.

The schedule is relative to the apply: reconcile re-sets the classifier
on every apply, so any filter change, node restart or link reset restarts
the window.

Verified on a two-container kernel link, 15/15: a single outage
[1000, 1500, 100] arrives per-seq as [0..4, 13..19] (passing before the
window, dropped inside, passing after); recurring 1000/2000 ms = 52 %
round trip (duty cycle); period == outage = permanent outage; period <
outage = 409 before uBridge; jittered flap keeps the ~50 % duty cycle;
30 % chance on a permanent window = 53 % round trip against the
per-direction theory 1-0.7^2 = 51 %; coexist with netem; node restart
restores; available_filters kernel vs relay (409 + hidden); teardown
clean. P6b re-run as a regression on the same uBridge build: 13/13.

Worth recording for the next rebuild: the first delivered window program
loaded as root but reported ebpf=0 through gns3-server — the verifier's
non-root path loses the loop counter's bound, treats the catch-up loop as
unbounded and rejects the *whole* program (E2BIG, 8193 pending states),
which also took frequency_drop and quota down, with ebpf=0 as the only
symptom. Smaller trip caps did not help; the loop had to go (uBridge
572ca0c), on top of a Makefile header-dependency fix (53e34bb) that had
been shipping a stale program object.

tests/controller/test_kernel_datapath_link.py

@@ -428,7 +428,7 @@ async def test_update_suspend_kernel_link_sends_no_synthetic_filter(project):
 async def test_kernel_datapath_eligible_with_netem_extension_filters(project):
     """
     All netem-extension types have a tc netem equivalent — they keep the
-    link kernel-eligible (only frequency_drop still forces the relay).
+    link kernel-eligible (kernel/relay is a purely topological choice).
     """
 
     link, node1, node2 = await _kernel_link(project)
@@ -441,6 +441,8 @@ async def test_kernel_datapath_eligible_with_netem_extension_filters(project):
         "gemodel": [100, 0, 30],
         "seed": [42],
         "limit": [5000],
+        "quota": [1000000, 100],
+        "window_drop": [0, 800, 100, 2400, 200],
     }
     # gemodel/packet_loss are mutually exclusive — drop packet_loss for the
     # eligibility check (validation rejects the mix elsewhere)
@@ -469,9 +471,9 @@ async def test_update_netem_extension_filters_accepted_on_kernel_link(project):
 @pytest.mark.asyncio
 async def test_update_kernel_only_filters_rejected_on_relay_link(project):
     """
-    Netem-extension / quota filters have no relay equivalent: setting them
-    on a created relay link is a 409. (The link is relay-wired because the
-    endpoints are mixed node types.)
+    Netem-extension / quota / window_drop filters have no relay equivalent:
+    setting them on a created relay link is a 409. (The link is relay-wired
+    because the endpoints are mixed node types.)
     """
 
     link, _n1, _n2 = await _relay_link(project)
@@ -481,6 +483,11 @@ async def test_update_kernel_only_filters_rejected_on_relay_link(project):
 
     with pytest.raises(ControllerError, match="kernel-datapath"):
         await link.update_filters({"rate": ["512kbit"]})
+    with pytest.raises(ControllerError, match="kernel-datapath"):
+        await link.update_filters({"window_drop": [0, 800, 100, 2400]})
+    with pytest.raises(ControllerError, match="period must be greater than or equal"):
+        # cross-parameter rule mirrors the tc window grammar
+        await link.update_filters({"window_drop": [0, 2000, 100, 1000]})
     # the stored filters are untouched
     assert link.filters == {}
 
@@ -489,6 +496,24 @@ async def test_update_kernel_only_filters_rejected_on_relay_link(project):
     assert link.filters == {"frequency_drop": [7]}
 
 
+@pytest.mark.asyncio
+async def test_update_window_drop_accepted_on_kernel_link(project):
+    """
+    window_drop rides the kernel NIO to both endpoints — including the
+    start=0 form (an immediate outage is NOT an "inactive" filter).
+    """
+
+    link, node1, node2 = await _kernel_link(project)
+    await link._prepare()
+
+    filters = {"window_drop": [0, 800, 100, 2400, 200]}
+    await link.update_filters(filters)
+    assert link.filters == filters
+    by_node = {entry[0].id: entry[3] for entry in (await link._prepare())}
+    assert by_node[node1.id]["filters"] == filters
+    assert by_node[node2.id]["filters"] == filters
+
+
 @pytest.mark.asyncio
 async def test_update_kernel_only_filters_accepted_before_creation(project):
     """